Plasma display and method of producing phosphor used therein

ABSTRACT

The present invention relates to a plasma display device and to a method of producing a phosphor to be used for the device, that prevents the phosphor layer from deteriorating, and improves the luminance, life, and reliability, of the PDP. The plasma display device is equipped with a plasma display panel in which a plurality of discharge cells are arranged, phosphor layers ( 110 R,  110 G,  110 B) in color corresponding to each discharge cell are allocated, and phosphor layers ( 110 R,  110 G,  110 B) are excited by ultraviolet light to emit light. Green phosphor layer ( 110 G) has a green phosphor including Zn 2 SiO 4 :Mn, the element ratio of zinc (Zn) to silicon (Si) is 2/1 to 2.09/1 at least at the proximity of the surface, and the layer is positively charged or zero-charged.

TECHNICAL FIELD

The present invention relates to a plasma display device having phosphorlayers that are excited by ultraviolet light to emit light, and to amethod of producing a phosphor used for the device.

BACKGROUND ART

In recent years, plasma display devices using plasma display panels(hereinafter, referred to as “PDP” or “panel”) receive attention ascolor display devices that implement large screen size, thin body, andlight weight in displaying color images for computers, television sets,and the like.

A plasma display device displays full color by means of additive colormixing of so-called three primary colors (red, green, and blue). Fordisplaying full color, a plasma display device is provided with phosphorlayers that emit light in the three primary colors: red (R), green (G),and blue (B). Phosphor particles composing the phosphor layers areexcited by ultraviolet light occurring in a discharge cell of the PDP,to generate visible light in each color.

Compounds used for the above-mentioned phosphors in each color include(YGd)BO₃:Eu³⁺ and Y₂O₃:Eu³⁺ for emitting red light; Zn₂SiO₄:Mn²⁺ forgreen; and BaMgAl₁0.0O₁₇:Eu²⁺ for blue. These phosphors, after given rawmaterials being mixed therewith, are produced with solid-phase reactionby being fired at a temperature above 1,000° C. This method is disclosedin “Phosphor Handbook (in Japanese)” (p. 219 and p. 225, by Ohmsha,Ltd., 1991), for example.

The phosphor particles produced by firing, after lightly crushed to theextent of breaking aggregated particles but not the crystals, arescreened (average particle diameter for red and green: 2 μm to 5 μm, forblue: 3 μm to 10 μm) before using. The reason for lightly crushing andscreening (classifying) phosphor particles is as follows. That is,methods of forming a phosphor layer in a PDP include screen-printing ofpasted phosphor particles in each color, and ink-jet method, in whichthe paste is discharged through a nozzle for applying. Largeagglomerates are included in a phosphor unless the phosphor particlesare classified after lightly crushed, and thus unevenness in coating andclogging in the nozzle may occur when coating the paste with thephosphors. Therefore, phosphors classified after being lightly crushedare small in particle diameter and even in particle size distribution,thus yielding a more desirable coated surface.

An example method of producing a green phosphor made of Zn₂SiO₄:Mn isdisclosed in “Phosphor Handbook (in Japanese)” (pp. 219-220, Ohmsha,Ltd., 1991). That is, SiO₂ is blended in ZnO at the rate of 1.5ZnO/SiO₂,which is larger than its stoichiometric ratio (2ZnO/SiO₂), and thenfired at 1,200° C. to 1,300° C. in the air (at one atmospheric pressure)to produce a green phosphor. In this case, the surface of the Zn₂SiO₄:Mncrystal is covered with an excessive amount of SiO₂, and the phosphorsurface is negatively charged.

The fact that a green phosphor in a PDP, negatively charged with a highlevel, degrades in its discharge characteristic, is disclosed inJapanese Patent Unexamined Publications No. H11-86735 and No.2001-236893, for example. Further, it is known that ink-jet coating, inwhich coating is made continuously with ink for a negatively chargedgreen phosphor through a fine-bore nozzle, causes clogging in the nozzleand unevenness in coating. These are because ethyl cellulose in the inkis in particular presumably resistant to being adsorbed in the surfaceof the negatively charged green phosphor.

Further, there is a problem in which a negatively charged phosphorcauses ion collision of a negatively charged green phosphor withpositive ions of Ne, CH-base, or H occurring while discharging,deteriorating the luminance of the phosphor.

Meanwhile, some methods are formulated such as laminate-coatingpositively charged oxide for changing negative charge on the surface ofZn₂SiO₄:Mn to positive one, and mixing a positively charged greenphosphor for apparently positive charge. However, it is problematic thatlaminate-coating oxide causes a low luminance, and applying twodifferent kinds of phosphor with a different charge state tends togenerating clogging and unevenness in coating. In addition, there is amethod in which ZnO and SiO₂ are blended in advance at the ratio of 2:1or more (2/1 or more of Zn/Si in element ratio) when producingZn₂SiO₄:Mn, and ZnO is scattered (sublimed) in advance while firing,using the vapor pressure of ZnO higher than SiO₂, when firing thephosphor in the air or in nitrogen at one atmospheric pressure at 1,200°C. to 1,300° C. However, even in such a case, the proximity of thecrystal surface results in rich SiO₂ and is negatively charged by allmeans.

The present invention, in view of these problems, aims at preventingphosphor layers from deteriorating and at improving the luminance, life,and reliability of a PDP.

SUMMERY OF THE INVENTION

In order to achieve this purpose, the plasma display device of thepresent invention is equipped with a plasma display panel in which aplurality of discharge cells are arranged, phosphor layers are allocatedwith a color corresponding to each discharge cell, and the phosphorlayers are excited by ultraviolet light to emit light. The phosphorlayers include a green phosphor layer containing Zn₂SiO₄:Mn, and thegreen phosphor made of Zn₂SiO₄:Mn has the element ratio of zinc (Zn) tosilicon (Si) of 2/1 or more at least at the proximity of the surface,and Mn is used as an activator.

In such a makeup, phosphor particles in which the green phosphor crystalis positively charged or zero-charged allow the phosphor layer to beformed with an even coating, prevent the luminance degradation of thephosphor, and improve luminance, life, and reliability of the PDP.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view illustrating a state of a PDP with its front glasssubstrate removed, used for a plasma display device according to anembodiment of the present invention.

FIG. 2 is a perspective view illustrating the structure of the imagedisplay area of the PDP.

FIG. 3 is a block diagram of the plasma display device according to theembodiment of the present invention.

FIG. 4 is a sectional view illustrating the structure of the imagedisplay area of the PDP used for the plasma display device according tothe embodiment of the present invention.

FIG. 5 is an outline block diagram of an ink dispenser used for forminga phosphor layer of the PDP.

FIG. 6 is an outline sectional view of a firing oven used when actuallyfiring a green phosphor.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

In the present invention, ZnO, SiO₂, and MnO₂ are mixed as an activatorwhen producing a green phosphor made of Zn₂SiO₄:Mn having the zincsilicate crystal structure, then this mixture is pre-fired in the air at600° C. to 900° C. to produce pre-fired powder, and next the pre-firedpowder is actually fired at 1,000° C. to 1,350° C., completely shieldedwith ZnO powder, to produce Zn₂SiO₄:Mn.

The green phosphor made of Zn₂SiO₄:Mn, used for a PDP, is usuallyproduced with solid-phase reaction method, where SiO₂ is blended in ZnOat a rate larger than its stoichiometric ratio, for improving luminance.This results in the surface of the Zn₂SiO₄:Mn crystal being covered withSiO₂. However, even if produced at the stoichiometric ratio so that thesurface will not be covered with SiO₂, firing at 1,000° C. or highercauses ZnO at the proximity of the surface to be scattered (sublimed)early, due to the vapor pressure of ZnO higher than that of SiO₂,resulting in more SiO₂ on the surface of the phosphor. If fired at1,000° C. or lower so that ZnO will not be scattered (sublimed),although Zn₂SiO₄:Mn with its Zn/Si ratio of 2/1 is synthesized, ahigh-luminance phosphor is not produced due to its low crystallinity.

The present invention solves the above-mentioned problem with thefollowing method. That is, set the element ratio of ZnO to SiO₂ to beblended, between 2.1/1 and 2.0/1, put a mixture of Zn₂SiO₄:Mn into acrucible and completely enclose (shield) its periphery with ZnO in orderto prevent the ZnO from being scattered (sublimed), and then fire thecovering ZnO in an oven at a temperature slightly higher than that ofZn₂SiO₄:Mn in the crucible, in an atmosphere of N₂ (nitrogen), N₂—H₂(nitrogen-hydrogen), and/or N₂—O₂ (nitrogen-oxygen), to prevent the ZnOfrom being scattered (sublimed). In other words, enclose the peripheryof pre-fired Zn₂SiO₄:Mn powder with ZnO, set the temperature of this ZnOto a slightly higher one, and set the saturated vapor pressure at theZnO side at the firing temperature relatively high, to prevent the ZnOin the pre-fired Zn₂SiO₄:Mn powder from being scattered (sublimed).

Hereinafter, a description will be made for a method of producing aphosphor according to the present invention.

Methods of producing a phosphor body itself include the following. Thatis, one is solid-phase sintering, where an oxidized or carbonated rawmaterial, and flux are used. Another is liquid-phase method, where aprecursor of a phosphor is produced with hydrolysis of organometallicsalt or nitrate salt in an aqueous solution, or with coprecipitationthat precipitates organometallic salt or nitrate salt with alkali or thelike added, and then the precursor is heat-treated to produce pre-firedpowder. Yet another is liquid spraying, where an aqueous solution withraw materials for a phosphor added is sprayed in a heated oven.

The present invention reveals that using a phosphor precursor andpre-fired powder produced with any of the above methods prevent ZnO frombeing scattered: from its surface while firing, and are effective inimproving the characteristic of Zn₂SiO₄:Mn phosphor, if Zn₂SiO₄:Mn isshielded (Zn₂SiO₄:Mn powder is sealed with ZnO.) with ZnO while fired at1,000° C. or higher, and then actually fired at 1,000° C. to 1,350° C.

As an example for a method of producing a green phosphor, a descriptionwill be made for a process of producing a green phosphor withsolid-phase reaction method according to the present invention. Blendcarbonate and oxide as the raw materials, such as ZnO, SiO₂, and MnCO₃,with a slightly more amount of ZnO over SiO₂ as compared to the molarratio of the base material ((Zn_(1-x)Mn_(x))₂SiO₄) for a phosphor. (Theelement compounding ratio of ZnO to SiO₂ is 2.1/1 to 2.0/1.) Next, aftermixing the materials, pre-fire them at 600° C. to 900° C. for two tothree hours. Then put them into a crucible (made of Al₂O₃ or ZnO),enclose the periphery of the crucible containing the pre-fired powder,with ZnO powder or a ZnO crucible, and set the temperature in the ovenso that the temperature of the ZnO crucible or ZnO powder will berelatively higher. Next, fire them under this temperature setting (at1,000° C. to 1,350° C.) in an atmosphere of at least one of N₂, N₂—H₂,and N₂—O₂, to produce a green phosphor.

Alternatively, in liquid-phase method, where a phosphor is produced froman aqueous solution, the following process is employed. That is,dissolve organometallic salt (e.g. alkoxide, acetylacetone) or nitratesalt, into water in advance so that the element ratio of Zn/Si will be2.1/1 to 2.0/1, and then hydrolyze it to produce a coprecipitate(hydrate). Next, pre-fire it at 600° C. to 900° C. in the air. Afterthat, in the same way as in the aforementioned solid-phase reactionmethod, enclose the periphery of the crucible containing the pre-firedpowder, with ZnO powder or a ZnO crucible, and set the temperature inthe oven so that the temperature of the ZnO crucible or ZnO powder willbe relatively higher. Next, fire them under this temperature setting (at1,000° C. to 1,350° C.) in an atmosphere of at least one of N₂, N₂—H₂,and N₂—O₂, to produce a green phosphor.

In this way, when pre-fired powder produced with a slightly more amountof ZnO over SiO₂ as compared to the stoichiometric ratio is shieldedwith ZnO, and fired at 1,000° C. to 1,350° C., ZnO is prevented frombeing scattered (sublimed) from the surface of Zn₂SiO₄:Mn, because thevapor pressure of the ZnO used for shielding is higher than that of theZnO in the pre-fired powder. Therefore, unlike conventional Zn₂SiO₄:Mn,the proximity of the surface does not result in rich SiO₂, butZn₂SiO₄:Mn with slightly rich ZnO, extending to the inside is produced.This allows producing a green phosphor with its Zn₂SiO₄:Mn particlesfavorably charged positively.

Here, the reason for limiting the ratio of Zn to Si to between 2.1/1 and2.0/1 is to facilitate positively charging Zn₂SiO₄ by means of aslightly excessive amount of Zn elements. Further, with the Zn ratio of2.1 or more, the amount of Zn in the crystal lattice increases to lowerthe luminance, while with 2.0 or less, Zn₂SiO₄ tends to be chargednegatively. Accordingly, the ratio of Zn to Si is desirably between2.1/1 and 2.0/1.

The reason for limiting the firing temperature to between 1,000° C. and1,350° C. is the following. That is, at 1,000° C. or lower, the vaporpressures of both ZnO and SiO₂ are low, and thus a small amount of ZnOis scattered (sublimed) from the surface, resistant to generating aSiO₂-rich layer at the proximity of the surface. However, ahigh-luminance phosphor is not produced due to poor crystallization ofZn₂SiO₄:Mn. Meanwhile, at 1,350° C. or higher, the vapor pressure of ZnObecomes relatively high as compared to that of SiO₂. This causescovering Zn₂SiO₄:Mn with ZnO less effective. Besides, excessivelysintered Zn₂SiO₄ causes a large particle diameter, lowering theluminance.

Next, a description will be made for a phosphor in each color used for aplasma display device according to the present invention. Concretephosphor particles used for a green phosphor layer are desirably thosemade from [(Zn_(1-x)Mn_(x))₂SiO₄] produced with the aforementionedmethod, and the value of x satisfies 0.01≦x≦0.2, for advantages inluminance and luminance degradation.

For concrete phosphor particles used for a blue phosphor layer, acompound expressed by Ba_(1-x)MgAl₁₀O₁₇:Eu_(x) orBa_(1-x-y)Sr_(y)MgAl₁₀O₁₇:Eu_(x) can be utilized. Here, the values x andy of the compound are desirably 0.03≦x≦0.20, and 0.1≦y≦0.5,respectively, for high luminance.

For concrete phosphor particles used for a red phosphor layer, acompound expressed by Y_(2x)O₃:Eu_(x) or (Y, Gd)_(1-x)BO₃:Eu_(x) can beutilized. Here, the value x of the compound for a red phosphor isdesirably 0.05≦x≦0.20, for advantages in luminance and luminancedegradation.

Hereinafter, a description will be made for an embodiment of a plasmadisplay device according to the present invention, referring todrawings.

FIG. 1 is a plan view illustrating a state of a PDP with its front glasssubstrate removed, used for the plasma display device according to theembodiment of the present invention. FIG. 2 is a perspective viewillustrating the structure of the image display area of the PDP. Here,FIG. 1 shows display electrodes, display scan electrodes, and addresselectrodes, with some of them omitted so as to be easily understood.

As shown in FIG. 1, PDP 100 is composed of front glass substrate 101(not illustrated), rear glass substrate 102, N pieces of displayelectrode 103, N pieces of display scan electrode 104 (N is affixed forshowing the Nth one), a group of M pieces of address electrode 107 (M isaffixed for showing the Mth one), and hermetic seal layer 121 shown byoblique lines. PDP 100 has an electrode matrix with a three-electrodestructure composed of display electrode 103, display scan electrode 104,and address electrode 107; and a display cell is formed at theintersecting point of display electrode 103 and display scan electrode104, and address electrode 107, forming image display area 123.

This PDP 100, as shown in FIG. 2, is composed of a front panel allocatedwith display electrode 103, display scan electrode 104, dielectric glasslayer 105, and MgO protective layer 106, all on one main surface offront glass substrate 101; and a back panel allocated with addresselectrode 107, dielectric glass layer 108, barrier rib 109, and phosphorlayers 110R, 110G, and 110B, all on one main surface of rear glasssubstrate 102. PDP 100 has a structure in which discharge gas isencapsulated in discharge space 122 formed between the front panel andthe back panel, and is connected to PDP driver 150 shown in FIG. 3, tocompose a plasma display device.

As shown in FIG. 3, the plasma display device has display driver circuit153, display scan driver circuit 154, and address driver circuit 155,all in PDP 100. A discharge voltage is applied to display scan electrode104 and address electrode 107 corresponding to a cell to be emitted,under control of controller 152, to perform address discharge betweenthe electrodes. After that, a pulse voltage is applied between displayelectrode 103 and display scan electrode 104 to perform sustaindischarge. This sustain discharge causes ultraviolet light to occur at arelevant cell. A phosphor layer excited by this ultraviolet light emitslight, to light the cell. A combination of emitted and non-emitted cellsin each color displays an image.

Next, a description will be made for a method of producing theabove-mentioned PDP 100, referring to FIGS. 4 and 5. FIG. 4 is asectional view illustrating the structure of the image display area ofthe PDP used for the plasma display device according to the embodimentof the present invention. In FIG. 4, the front panel is produced in thefollowing way. That is, after forming display electrode 103 and displayscan electrode 104, N pieces each (Only two pieces each are shown inFIG. 2.), alternately and parallel in a striped form on front glasssubstrate 101, cover the top of them with dielectric glass layer 105,and further form MgO protective layer 106 on the surface of dielectricglass layer 105.

Display electrode 103 and display scan electrode 104 are composed of atransparent electrode made of indium tin oxide (ITO) and a bus electrodemade of silver. The silver paste for the bus electrode is formed bybeing applied with screen-printing and then fired.

Dielectric glass layer 105 is formed so that it will have a giventhickness (approximately 20 μm), from a paste including a lead-basedglass material being applied with screen-printing and then fired at agiven temperature for a given time (at 560° C. for 20 minutes, forexample). A paste including the above-mentioned lead-based glassmaterial is, for example, a mixture of PbO (70 wt %), B₂O₃ (15 wt %),SiO₂ (10 wt %), Al₂O₃ (5 wt %), and an organic binder (10% ethylcellulose dissolved in alpha-terpineol). Here, an organic binder means aresin dissolved in an organic solvent, where an acrylic resin, besidesethyl cellulose, can be used as a resin, and butylcarbitol or the likecan be also used as an organic solvent. Further, such a organic bindermay immix glyceryl trileate, for example.

MgO protective layer 106, made of magnesium oxide (MgO), is formed sothat the layer will have a given thickness (approximately 0.5 μm) with amethod such as sputtering or chemical vapor deposition (CVD).

The back panel is formed into a state where M pieces of addresselectrodes 107 are installed in a row, from a silver paste forelectrodes being screen-printed onto rear glass substrate 102 and thenfired. A paste including a lead-based glass material is applied on theback panel with screen-printing to form dielectric glass layer 108. Inthe same way, barrier rib 109 is formed from a paste including alead-based glass material being applied repeatedly at a given pitch withscreen-printing and then fired. This barrier rib 109 partitionsdischarge space 122 line-wise into each cell (unit of light-emittingregion). Further, W, which is the gap between barrier ribs 109, isdefined as between approximately 130 μm and 240 μm according tohigh-definition TV with its screen size between 32 inches and 50 inches.

In addition, phosphor layer in red (R), blue (B), green (G) are formedin the grooves between barrier ribs 109. Green phosphor layer 110G isformed with a green phosphor, which is pre-fired Zn₂SiO₄:Mn powder withits element ratio of Zn/Si of 2.1/1 to 2.0/1, the periphery of which isshielded with ZnO, fired at 1,000° C. to 1,350° C. in an atmosphere ofat least one of N₂, N₂—O₂, and N₂—H₂.

Phosphor layers 110R, 110G, and 110B, where phosphor particles are boundeach other, are formed from a phosphor ink paste made of phosphorparticles and an organic binder being applied and then fired at 400° C.to 590° C. to burn out the organic binder. It is desirable to formphosphor layers 110R, 110G, and 110B, so that L, which is thelamination-wise thickness of the layers on address electrode 107, willbe roughly 8 to 25 times the average particle diameter of the phosphorparticles in each color. In other words, the phosphor layer desirablyretains a thickness of at least 8 layers, and preferably about 20 layersof lamination, in order not to let ultraviolet light generated in thedischarge space transmit but to be eliminated, for ensuring luminance(emission efficiency), when irradiating the phosphor layer with acertain amount of ultraviolet light. This is because the emissionefficiency of the phosphor layer is almost saturated, and the size ofdischarge space 122 cannot be adequately ensured with a thickness morethan the above.

Meanwhile, phosphor particles small enough in their diameter andspherical, such as those produced with hydrothermal synthesis method orthe like, raise the filling density of the phosphor layers and increasethe total surface area of the phosphor particles, as compared to thecase of unspherical particles and the same levels of lamination.Consequently, the surface area of phosphor particles involved in actuallight-emitting increases, further raising the emission efficiency.

The front and back panels produced in this way are overlapped each otherso that respective electrodes on the front panel will be orthogonalizedwith the address electrodes on the back panel. In addition, the panelsare sealed with sealing glass inserted to the periphery of the panelsand then fired at approximately 450° C. for 10 to 20 minutes, forexample, to form hermetic seal layer 121. Next, after the inside ofdischarge space 122 is once exhausted to a high vacuum (e.g. 1.1×10⁻⁴Pa), discharge gas such as an He—Xe-based or He—Xe-based inactive gas isencapsulated at a given pressure, producing PDP 100.

FIG. 5 is an outline block diagram of ink dispenser 200 used whenforming phosphor layers 110R, 110G, and 110B. As shown in FIG. 5, inkdispenser 200 includes server 210, pressure pump 220, and header 230.Phosphor ink supplied from server 210 for storing phosphor ink,pressurized by pressure pump 220, is supplied to header 230. Header 230is provided with ink chamber 230 a and nozzle 240, and the pressurizedphosphor ink supplied to ink chamber 230 a is discharged continuouslythrough nozzle 240. D, which is the bore of this nozzle 240, isdesirably 30 μm or more for preventing clogging in the nozzle and isequal to W (approximately 130 μm to 200 μm) or less, where W is the gapbetween barrier ribs 109, for preventing the nozzle from protruding frombarrier rib 109 when applying, where it is set usually between 30 μm to130 μm.

Header 230 is linearly driven by a header scanning mechanism (notillustrated). Having header 230 scan as well as continuously dischargingphosphor ink 250 through nozzle 240 allows the phosphor ink to beuniformly applied to the grooves between barrier ribs 109 on rear glasssubstrate 102. Here, the viscosity of the phosphor ink used ismaintained between 1,500 centipoise (CP) and 50,000 CP at 25° C.

Still, above-mentioned server 210 is equipped with an agitation device(not illustrated), which prevents the particles in the phosphor ink frombeing precipitated. Further, header 230 is integrally molded with inkchamber 230 a and nozzle 240 included, and is produced from a metallicmaterial with machining and electric discharging

Further, a method of forming a phosphor layer is not limited to theabove-mentioned method, but various methods can be used such asphotolithographic method, screen-printing, and a method in which a filmwith phosphor particles mixed is allocated.

Phosphor ink is a mixture of phosphor particles in each color, a binder,and solvent, all blended so that the viscosity will range between 1,500centipoise (CP) and 50,000 CP, where a surface active agent, silica,dispersant (0.1 wt % to 5 wt %), and others may be added as required.

A red phosphor blended in this phosphor ink is a compound expressed by(Y, Gd)_(1-x)BO₃:Eu_(x) or Y_(2x)O₃:Eu_(x). These are compounds in whichEu is substituted for a part of Y element composing its maternalmaterial. Here, x, which is the substitution value of Eu element for Yelement, desirably ranges as 0.05≦x≦0.20. For a substitution value morethan this, the luminance significantly degrades, although it increases,which is assumed to be impractical. Meanwhile, for a substitution valueless than this, the composition ratio of Eu, the main element oflight-emitting, decreases, so does the luminance, making useless as aphosphor.

A green phosphor uses a compound expressed by [(Zn_(1-x)Mn_(x))₂SiO₄],that is pre-fired with its element ratio of Zn/Si of 2.1/1 to 2.0/1, andthen fired in an atmosphere of N₂, N₂—H₂, and/or N₂—O₂, shielded withZnO. [(Zn_(1-x)Mn_(x))₂SiO₄] is a compound in which Mn is substitutedfor a part of Zn element composing its maternal material. Here, x, whichis the substitution value of Mu element for Zn element, desirably rangesas 0.01≦x≦0.20.

A blue phosphor uses a compound expressed by Ba_(1-x)MgAl₁₀O₁₇:Eu_(x) orBa_(1-x-y)Sr_(y)MgAl₁₀O₁₇:EU_(x). Ba_(1-x)MgAl₁₀O₁₇:Eu_(x) andBa_(1-x-y)Sr_(y)MgAl₁₀O₁₇:Eu_(x) are compounds in which Eu or Sr issubstituted for a part of Ba element composing its maternal material.Here, x and y, which are substitution values of Eu element for Baelement, desirably range as 0.03≦x≦0.20 and 0.1≦y≦0.5.

Further, as a binder blended in a phosphor ink, ethyl cellulose oracrylic resin (0.1 wt % to 10 wt % of ink is mixed) can be used; and asa solvent, alpha-terpineol or butylcarbitol can be used. Here, thebinder may be polymer molecules such as PMA or PVA, and the solvent maybe an organic solvent such as diethylene glycol or methyl ether.

In this embodiment, phosphor particles are manufactured with solid-phasereaction method, aqueous solution method, spray firing method, orhydrothermal synthesis method. A concrete example for a method ofproducing phosphor particles will be hereinafter described.

First, a description will be made for a method of producing a bluephosphor of Ba_(1-x)MgAl₁₀O₁₇:Eu_(x) with aqueous solution method.

In the process of producing a mixed solution, mix the raw materials ofbarium nitrate Ba(NO₃)₂, magnesium nitrate Mg(NO₃)₂, aluminium nitrateAl(NO₃)₃, and europium nitrate Eu(NO₃)₂, with the molar ratio of1-x:1:10:x (0.03≦x≦0.25), and dissolve them into an aqueous medium toproduce a mixed solution. This aqueous medium is desirably ion-exchangedwater or pure water in that they do not include an impure substance;however, they can be used even if they include a nonaqueous solvent(e.g. methanol, ethanol). Next, put the hydrate liquid mixture into acontainer made of a material with resistance to corrosion and heat, suchas gold or platinum, and then use a device capable of heating underpressure, such as an autoclave, to perform hydrothermal synthesis (for12 to 20 hours) at a given temperature (100° C. to 300° C.), at a givenpressure (0.2 MPa to 10 MPa), in a high-pressure container. Next, firethis powder in a reducing atmosphere (e.g. atmosphere including 5% ofhydrogen and 95% of nitrogen) at a given temperature, for a given time(e.g. at 1,350° C. for two hours), and classify this, to produce adesired blue phosphor Ba_(1-x)MgAl₁₀O₁₇:Eu_(x).

Phosphor particles produced with hydrothermal synthesis are sphericaland have particle diameters smaller than those produced with theconventional solid-phase reaction, resulting in an average particlediameter of approximately 0.05 μm to 2.0 μm. Here, “spherical” isdefined as the aspect ratio (minor axis diameter/major axis diameter) ofmost phosohor particles ranges between 0.9 and 1.0, for example, whereall the phosphor particles do not necessarily fall in this range.

Meanwhile, a blue phosphor can be produced with spraying also, in whichthe hydrate mixture is not put into a gold or platinum container, butthe mixture is sprayed through a nozzle to a high-temperature oven, tosynthesize a phosphor.

Next, a description will be made for a method of producing a bluephosphor of Ba_(1-x-y)Sr_(y)MgAl₁₀O₁₇:Eu_(x) manufactured withsolid-phase reaction method.

Weigh raw materials of barium hydroxide Ba(OH)₂, strontium hydroxideSr(OH)₂, magnesium hydroxide Mg(OH)₂, aluminum hydroxide Al(OH)₃, andeuropium hydroxide Eu(OH)₂, for a required molar ratio, and mix themalong with AlF₃ as flux. After that, fire them at a given temperature(1,300° C. to 1,400° C.), for a given time (12 to 20 hours) to produceBa_(1-x-y)Sr_(y)MgAl₁₀O₁₇:Eu_(x) in which quadrivalent ions aresubstituted for Mg and Al. The average particle diameter of the phosphorparticles produced with this method is approximately 0.1 μm to 3.0 μm.Next, after firing these in a reducing atmosphere, 5% hydrogen and 95%nitrogen, for example, at a given temperature (1,000° C. to 1600° C.),for a given time (two hours), classify them with an air classifier toproduce phosopher powder.

Here, oxide, nitrate salt, and hydroxide are mainly used as rawmaterials for a phosphor. However, a phosphor can be produced also withan organometallic compound including elements such as Ba, Sr, Mg, Al,and Eu (e.g. metal alkoxide and acetylacetone).

Next, a description will be made for a method of producing a greenphosphor of (Zn_(1-x)Mn_(x))₂SiO₄. FIG. 6 is an outline sectional viewof a firing oven used when actually firing a green phosphor. In FIG. 6,firing oven body 300, a kind of electric oven, is composed of firstcrucible 310 made of ZnO or Al₂O₃; ZnO powder 330, enclosing crucible310; second crucible 350 made of ZnO or Al₂O₃, containing first crucible310 and ZnO powder 330; and heater 340 provided on the outer edge, wherefirst crucible 310 contains pre-fired phosphor powder 320 therein.

First, a description will be made for the case where a green phosphor isproduced with solid-phase method. Mix the raw materials of zinc oxide(ZnO), silicon oxide (SiO₂), and manganese oxide MnO, so that the molarratio of Zn to Mn will be 1:x:x (0.01≦x≦0.20), and next mix the rawmaterials along with flux (ZnF₂ and MnF₂) as required, so that theelement ratio of Zn to Si will be 2.1/1 to 2.0/1. Pre-fire this mixtureat 650° C. to 900° C. for two hours. Next, lightly crush the mixture tothe extent of breaking the agglomerate, put it into first crucible 310made of Al₁O₃ or ZnO, enclose it with ZnO powder 330 and ZnO crucible350, and fire them in an atmosphere including at least one of N₂, N₂—O₂,and N₂—H₂, at 1,000° C. to 1,350° C., to produce a green phosphor. Atthis moment, if an arrangement is made so that heater 340 of the ovenwill be located at the periphery of second crucible 350 made of ZnOand/or ZnO powder 330, the temperature of first crucible 310, secondcrucible 350, and ZnO powder 330 can be made slightly higher than thatof pre-fired phosphor powder 320 made of Zn₂SiO₄:Mn. Power control ofheater 340 at the periphery of second crucible 350, and flow adjustmentof an ambient gas of N₂, N₂—O₂, and/or N₂—H₂ control the respectivetemperatures of second crucible 350, first crucible 310, ZnO powder 330,and pre-fired phosphor powder 320 of Zn₂SiO₄:Mn, for actually firing.Here, in this embodiment, the description is made for the case where anelectric oven is used. However, a gas oven or the like may be used.

Next, a description will be made for the case where a green phosphor isproduced with aqueous solution method. In the process of producing amixed solution, mix the raw materials of zinc nitrate Zn(NO₃)₂,manganese nitrate Mn(NO₃)₂, and ethyl silicate[Si(O.C₂H₅)₄], so that themolar ratio of zinc nitrate to manganese nitrate will be 1-x:x(0.01≦x≦0.20). Next, in blending Zn(NO₃)₂ and [Si(O.C₂H₅)₄], mix the rawmaterials so that the element ratio of Zn to Si will be 2.1/1 to 2.0/1,and put them into ion-exchanged water to produce a mixed solution. Next,in hydration process, drop a basic aqueous solution such as an aqueousammonia solution into this mixed solution to form hydrate. Pre-fire thishydrate at 600° C. to 900° C., and next, in the same way as insolid-phase method, put this pre-fired matter in first crucible 310 madeof Al₂O₃ or ZnO, enclose the periphery of this first crucible 310 withZnO powder 330 and second crucible 350 in an atmosphere of N₂, N₂—O₂,and/or N₂—H₂ at 1,000° C. to 1,350° C., to produce a green phosphor.

Next, a description will be made for a method of producing a redphosphor with aqueous solution method.

First, a red phosphor of (Y, Gd)_(1-x)BO₃:Eu_(x) will be described. Inthe process of producing a mixed solution, mix the raw materials ofyttrium nitrate Y₂(NO₃)₃, hydro nitrate gadolinium Gd₂(NO₃)₃, boric acidH₃BO₃, and europium nitrate Eu₂(NO₃)₃, so that the molar ratio will be1-x:2:x (0.05≦x≦0.20) (The ratio of Y to Gd is 65:35), and afterheat-treating them at 1,200° C. to 1,350° C. in the air, classify themto produce a red phosphor.

Meanwhile, for a red phosphor of Y_(2x)O₃:Eu_(x), in the process ofproducing a mixed solution, dissolve the raw materials of yttriumnitrate Y₂(NO₃)₂ and europium nitrate Eu(NO₃)₂ into ion-exchanged water,so that the molar ratio will be 2-x:x (0.05≦x≦0.30), to produce a mixedsolution. Next, in hydration process, add a basic aqueous solution (e.g.aqueous ammonia solution) to this aqueous solution to form hydrate.After that, in hydrothermal synthesis process, put the hydrate andion-exchanged water into a container with resistance to corrosion andheat, such as platinum or gold, and then perform hydrothermal synthesisin a high-pressure container such as an autoclave, at 100° C. to 300° C.at a pressure of 0.2 MPa to 10 MPa for 3 to 12 hours. After that, drythe yielded compound to produce desired Y_(2x)O₃:Eu_(x). Next, afterannealing this phosphor in the air at 1,300° C. to 1,400° C. for twohours, classify it to form a red phosphor.

Here, the above-mentioned phosphor layers 110R and 110B of PDP 100 usethose having been used conventionally, and phosphor layer 110G usesgreen phosphor particles with its surface of [(Zn_(1-x)Mn_(x))₂SiO₄]composing the positively charged phosphor.

EVALUATION EXPERIMENT

Hereinafter, in order to evaluate the performance of the plasma displaydevice according to the present invention, an evaluation experiment ismade for a sample device using a phosphor according to theabove-mentioned embodiment.

The respective plasma display devices are produced so that they willhave 42-inch size (specification of high-definition TV with its ribpitch of 150 μm), the thickness of the dielectric glass layer is 20 μm,the thickness of the MgO protective layer is 0.5 μm, and the distancebetween the display electrode and display scan electrode is 0.08 mm.Further, the discharge gas to be encapsulated in the discharge space isa neon-based gas with a xenon gas mixed by 5%, encapsulated at a givendischarge-gas pressure.

Zn₂SiO₄:Mn green phosphor particles used for sample plasma displaydevices 1 through 10 adopt a [(Zn_(1-x)Mn_(x))₂SiO₄] phosphor producedas follows: That is, put pre-fired powder of a phosphor with its elementratio of Zn to Si of 2.1/1 to 2.0/1 into first crucible 310 made ofAl₂O₃ or ZnO, enclose the periphery of this crucible with ZnO powder 330and second crucible 350, and then fire them in an atmosphere of N₂,N₂—O₂, and/or N₂—H₂ at 1,000° C. to 1,350° C. Table 1 shows theconditions of synthesis for each phosphor used in these samples. TABLE 1Element ratio of Zn/Si Pre-firing Firing atmosphere Crucible for pre-Sample Amount of as raw temperature and firing fired powder and numberMn: x materials (° C.) temperature its arrangement Green phosphor[(Zn_(1.x)Mn_(x))₂SiO₄] Solid-phase method 1 x = 0.02 2.1/1 In the air,In N₂, 1,200° C., ZnO crucible, cover 600° C., 2 3 hours the peripherywith hours ZnO powder 2 x = 0.05 2.07/1  In the air, In N₂—H₂, 1,350°C., Al₃O₂ crucible, cover 750° C., 2 3 hours the periphery with hoursZnO powder 3 X = 0.1 2.04/1  In the air, In N₂, 1,150° C., ZnO crucible,cover 850° C., 2 3 hours the periphery with hours ZnO powder 4 X = 0.22.0/1 In the air, In N₂—O₂ 1,000° C., Cover ZnO crucible with 900° C., 210 hours ZnO crucible and fill hours therebetween with ZnO Greenphosphor [(Zn_(1.x)Mn_(x))₂SiO₄] Liquid-phase method 5 x = 0.01 2.0/1 Inthe air, In N₂, 1,300° C., ZnO crucible, cover 700° C., 3 3 hours theperiphery with hours ZnO powder 6 x = 0.03 2.03/1  In the air, (same asthe above) (same as the above) 800° C., 3 hours 7 x = 0.05 2.01/1  (sameas the (same as the above) (same as the above) above) 8 x = 0.1 (same asthe (same as the (same as the above) (same as the above) above) above) 9x = 0.05 (same as the (same as the (same as the above) (same as theabove) above) above) 10* (same as the 1.9/1 (same as the (same as theabove) (same as the above) above) above) 11* (same as the 2.2/1 (same asthe (same as the above) (same as the above) above) above) 12* (same asthe 2.0/1 (same as the (same as the above) Put only pre-fired above)above) powder into Al₃O₂ crucible 13* (same as the (same as the (same asthe In N₂—O₂ 900° C., ZnO crucible, cover above) above) above) 10 hoursthe periphery with ZnO powder Sample Amount of Method of Amount ofMethod of number Eu: X manufacturing Mn: x manufacturing Red phosphorBlue phosphor [(Y, Gd)_(1.x)BO₃:Eu_(x)] [Ba_(1.x)MgAl₁₀O₁₇:Eu_(x)] 1 x =0.1 Solid-phase x = 0.1 Solid-phase reaction reaction method method 2 x= 0.2 (same as the 1 = 0.2 (same as the above) above) 3 x = 0.3 Aqueousx = 0.5 (same as the solution above) method 4 x = 0.15 (same as the x =0.1 (same as the above) above) Red phosphor Blue phosphor[(Y_(1.x))₂O₃:Eu_(x)] [Ba_(1.x.y)Sr_(y)MgAl₁₀O₁₇:Eux] 5 x = 0.01 Aqueousx = 0.2, Aqueous solution y = 0.1 solution method method 6 X = 0.1 (sameas the x = 0.3, (same as the above) y = 0.3 above) 7 X = 0.15 (same asthe x = 0.4, (same as the above) y = 0.5 above) 8 x = 0.2 Solid-phase x= 0.5, (same as the reaction y = 0.3 above) method 9 (same as the (sameas the x = 0.15, (same as the above) above) y = 0.5 above) 10* (same asthe (same as the (same as the (same as the above) above) above) above)11* (same as the (same as the (same as the (same as the above) above)above) above) 12* (same as the (same as the (same as the (same as theabove) above) above) above) 13* (same as the (same as the (same as the(same as the above) above) above) above)*Sample numbers 10 through 13 are for comparative examples.

In samples 1 through 4, a green phosphor is a combination using(Zn_(1-x)Mn_(x))₂SiO₄ produced with solid-phase synthesis method; a redphosphor, (Y, Gd)_(1-x)BO₃:Eu_(x); and a blue phosphor,(Ba_(1-x)MgAl₁₀O₁₇:Eu_(x)). Each sample shows variation in method ofsynthesizing a phosphor; substitution ratios of Mn and Eu, which are themain elements for light-emitting, namely substitution ratio of Mn to Znelement and substitution ratio of Eu to Y and Ba elements; and elementratio of Zn to Si and firing conditions for a green phosphor, as shownin table 1.

In samples 5 through 9, a green phosphor is a combination using(Zn_(1-x)Mn_(x))₂SiO₄ produced with liquid-phase method (aqueoussolution method); a red phosphor, (Y_(1-x))₂O₃:Eu_(x); and a bluephosphor, B_(1-x-y)Sr_(y)MgAl₁₀O₁₇:Eu_(x). Each sample shows variationin method of synthesizing a phosphor; and element ratio of Zn to Si andfiring conditions for a green phosphor, as shown in table 1.

Further, phosphor ink used for forming a phosphor layer is produced bymixing a phosphor, resin, solvent, and dispersant, using each phosphorparticle shown by table 1.

The measurement result shows that the viscosity of the phosphor ink atthat time (25° C.) all remains in the range between 1,500 CP and 50,000CP. In all the phosphor layers formed, the side faces of the barrierribs are found by observation to be uniformly coated with phosphor ink.

Further, the bore of the nozzle used for coating then is 100 μm, andphosphor particles used for the phosphor layer have an average particlediameter of 0.1 μm to 3.0 μm and a maximum particle size of 8 μm orless.

Sample 10 is a comparative sample with its element ratio of Zn/Si of1.9/1 when blending raw materials for a green phosphor; and sample 11,in the same way, of Zn/Si of 2.2/1. Sample 12 is a green phosphor in theconventional example, with its element ratio of Zn/Si of 2.0/1 whenblending raw materials, fired only with a regular crucible (made ofAl₂O₃). In sample 13, the ratio of Zn/Si when blending raw materials fora green phosphor is 2.0/1, the firing temperature for pre-fired powderis the same as in the present invention, a crucible made of ZnO iscovered with ZnO powder, but the temperature when actually firing is setto as low as 900° C.

EXPERIMENT 1

Measurement is made of the charging tendency for the green phosphors ofsamples 1 through 9 and comparative sample 10. Here, the measurementadopts blow-off method, which measures the amount of charge for reducediron powder.

EXPERIMENT 2

Measurement is made of the element ratio of Zn to Si at the proximity(approximately 10 nm) of the surface with X-Ray photoelectronspectroscopy (XPS) for samples 1 through 9 and comparative sample 10produced.

EXPERIMENT 3

Measurement is made of the luminance of a PDP in fully white after thePDP producing process, and the luminance of green and blue phosphorlayers, with a luminance meter.

EXPERIMENT 4

Measurement is made of the luminance degradation factor when displayingfull white, green, and blue as follows: That is, continuously applydischarge sustain pulses with 185 V, 100 kHz, to a plasma display devicefor 1,000 hours, measure the luminance of the PDP before and after then,and calculate the luminance degradation factor (<[luminance afterapplication—luminance before application]/luminance before application>100)

An address error during address discharge is judged from at least asingle flicker on the screen.

EXPERIMENT 5

Clogging in the nozzle is checked when green phosphor ink is appliedusing a nozzle with its bore of 100 μm, for 100 hours continuously.

Table 2 shows experimental results of the luminance and luminancedegradation factor, and of clogging in the nozzle, for green phosphorsin experiments 1 through 5. Rate of luminance change (%) of panel afterdischarge sustain pulses with 185 V, Zn/Si ratio of green phosphor withLuminance of panel 100 kHz applied for 1,000 Sample XPS and chargingtendency in green hours Address error during Clogging in nozzle numberZn/Si ratio Charging endency Cd/cm² Green Blue address discharge (200hours) 1 2.09/1 + 250.0 −1.2 −2.9 No No 2 2.06/1 + 265.0 −1.5 −2.6 (sameas the ahove) (same as the above) 3 2.03/1 + 270.0 −1.1 −2.8 (same asthe above) (same as the above) 4 2.01/1 + 245.0 −1.3 −2.6 (same as theabove) (same as the above) 5 2.01/1 + 242.0 −1.5 0 (same as the above)(same as the above) 6 2.02/1 + 257.0 −1.8 −2.7 (same as the above) (sameas the above) 7  2.0/1 0 273.0 −1.7 −2.3 (same as the above) (same asthe above) 8  2.0/1 0 271.0 −1.9 −2.4 (same as the above) (same as theabove) 9  2.0/1 0 273.0 −1.6 −2.5 (same as the above) (same as theabove) 10* 1.90/1 − 253.0 −25.8 −4.8 Yes Yes 11* 2.19/1 + 203 −2.9 −3.6No No 12* 1.92/1 − 249 −28.3 −5.1 Yes Yes 13* 1.98/1 − 185 −18.6 −5(same as the above) (same as the above)*Sample numbers 10 through 13 are for comparative examples.

As shown in table 2, in comparative sample 10, the element ratio of Znto Si as raw materials is 1.9/1, and Si in Zn₂SiO₄:Mn is richer in theratio of Zn/Si as compared to the stoichiometric ratio. Therefore,sample 10 is negatively charged, the luminance of the panel in green andblue largely degrades, and an address error and clogging in the nozzleoccur. In sample 11, the ratio of Zn to Si as raw materials is 2.2/1,which means sample 11 is rich in Zn and the powder is positivelycharged. However, sample 11 is richer in Zn as compared to thestoichiometric ratio, and thus the phosphor becomes deteriorated incrystallization and the panel in blue has a low luminance. Meanwhile,comparative sample 12 is a green phosphor produced with the conventionalproducing method, and thus ZnO sublimes selectively from the surface,sample 12 is in Si with the Zn/Si ratio of 1.92/1, to be negativelycharged, the luminance of the panel in green in an accelerated lifelargely degrades, and an address error and clogging in the nozzle occur.In comparative sample 13, where the periphery of the first crucible iscovered with ZnO powder, the temperature for actually firing is as lowas 900° C., and thus Zn₂SiO₄:Mn is insufficiently crystallized, and thepanel has a low luminance and large luminance degradation for green.

Meanwhile, the green phosphors according to the present invention insamples 1 through 9, where Zn and Si are blended at the element ratio ofZn/Si of 2.0/1 to 2.1/1, pre-fired powder is put into a crucible, theperiphery of which is enclosed with ZnO powder, and produced at 1,000°C. to 1,350° C., are positively charged or zero-charged, and thus theluminance in green and blue slightly degrades, and an address error andclogging in the nozzle when applying phosphors do not occur. This ispresumably because positively charging or zero-charging the negativelycharged green phosphor causes the phosphor to be immune to an impact ofpositive ions such as neon ions (Ne⁺) and CH_(x)-based ions (CH_(x) ⁺)existing in the discharge space of the panel, suppressing luminancedegradation. Here, an impact of ions is slightly reduced for the bluephosphor also.

Further, the reason why address errors have been eliminated ishomogenization of address discharge as a result that the green phosphoris positively charged, which is the same as for the red and blue ones.Still, the reason why clogging in the nozzle has been eliminated ispresumanly the improved dispersibility of the phosphor ink because theethyl cellulose in the binder is prone to adsorbing a positively chargedgreen phosphor.

INDUSTRIAL APPLICABILITY

As above-mentioned, according to the present invention, a green phosphor(Zn_(1-x)Mn_(x))₂SiO₄ composing a phosphor layer is positively chargedor zero-charged, to homogenize coating condition, to preventdeterioration, of the phosphor layer, and also to improve luminance,life, and reliability, of the PDP, thus effectively improving theperformance of the plasma display device.

1. A plasma display device including a plasma display panel in which aplurality of discharge cells are arranged, and a phosphor layer in colorcorresponding to each discharge cell is allocated, and the phosphorlayer emits light by being excited by ultraviolet light, wherein thephosphor layer has a green phosphor layer including Zn₂SiO₄:Mn; and thegreen phosphor made of Zn₂SiO₄:Mn has an element ratio of zinc (Zn) tosilicon (Si) of 2/1 or more at least at a proximity of a surface, anduses Mn as an activator.
 2. A plasma display device including a plasmadisplay panel in which a plurality of discharge cells are arranged, anda phosphor layer in a color corresponding to each discharge cell isallocated, and the phosphor layer emits light by being excited byultraviolet light, wherein the phosphor layer has a green phosphor layerincluding Zn₂SiO₄:Mn; and the green phosphor made of Zn₂SiO₄:Mn has anelement ratio of zinc (Zn) to silicon (Si) of 2/1 to 2.09/1 at least ata proximity of a surface, and is positively charged or zero-charged. 3.A method of producing a phosphor for a plasma display device,comprising: a process in which, after dissolving one of nitrate salt andorganometallic salt, including elements [Zn, Si, Mn] composing a greenphosphor, in water, a coprecipitate is produced with hydrolysis; apre-firing process in which the coprecipitate is fired in an air at 600°C. to 900° C., to produce pre-fired matter; and a firing process inwhich the pre-fired substance is fired at 1,000° C. to 1,350° C., withbeing enclosed by ZnO powder.
 4. A method of producing a phosphor for aplasma display device, comprising: a process of mixing a raw materialfor a phosphor, in which a raw material of oxide and/or carbonateincluding elements [Zn, Si, Mn] composing a green phosphor, are mixed; apre-firing process in which the mixed raw material is fired in an air at600° C. to 900° C., to produce pre-fired matter; and a firing process inwhich the pre-fired substance is fired at 1,000° C. to 1,350° C., withbeing enclosed by ZnO powder.
 5. A method of producing a phosphor for aplasma display device as claimed in claim 3, wherein a temperature of alocation on which a pre-fired substance is arranged is lower than thatof a location on which ZnO powder is arranged.
 6. A method of producinga phosphor for a plasma display device as claimed in claim 4, wherein atemperature of a location on which a pre-fired substance is arranged islower than that of a location on which ZnO powder is arranged.